When cement- and lime-bonded building materials such as plaster, lime brick, fibre cement parts or concrete blocks, in particular roof tiles, paving stones or promenade tiles, are to be colored, the coloring materials used are generally inorganic pigments. The pigments conventionally used in the building materials industry are iron oxides or iron hydroxides for red, black, brown or yellow, manganese oxides for black-brown, chromium oxides for green and titanium dioxides for white. In addition, carbon blacks may be used as black pigments, nickel or chromium rutiles as yellow pigments, spinels containing cobalt as blue and green pigments, spinels containing copper as black pigments and mixed crystals of barium sulphate and barium manganate as blue pigments.
For coloring concrete materials, the pigments are generally used in powder form. When ground up as powders they have the advantage of being readily dispersible; such pigment powders can be distributed completely homogeneously in concrete mixtures within a short time of up to a few minutes. The disadvantage of these fine powders, however, is that they do not flow freely and in many cases cake together and form lumps when kept in storage. This renders accurate dosing difficult and another disadvantage of some powders is that they tend to form dust.
It is known that these disadvantages can be avoided in the pigmentation of concrete parts by using aqueous pigment suspensions instead of dry pigment powders. The use of such pastes or slurries containing 30 to 70% by weight of pigment, however, has only slowly become established as the additional water content may considerably increase the transport costs, depending on the distance between the place of manufacture and the building site. Moreover, not all concrete preparations are capable of absorbing the large quantity of water carried with the pigment.
The building materials industry has therefore for the most part continued to use dry pigment powders. The use of pigments in the form of microgranulates such as are commonly used in the plastics and lacquer industry has hitherto been prevented by the commonly held belief that granulates are not easily dispersible in concrete preparations. Pigment agglomerates which are not easily dispersible require substantially longer mixing times. In the short mixing times conventionally used in the manufacture of building materials, patches, streaks and nests of color occur on the surface of the concrete due to imperfect pigment distribution. The intensity of color contained in the pigment cannot fully develop, with the result that larger quantities of pigment are required for obtaining a given intensity of color in the concrete.
Pigment granulates consisting substantially of pigment and one or more binders which promote dispersion of the pigment in the concrete are described in DE-C 3 619 363 for coloring concrete. The following are mentioned there as binders which function as dispersing auxiliaries in concrete: Alkyl benzene sulphonates, alkyl naphthalene sulphonates, lignin sulphonate, sulphated polyglycol ethers, melamine formaldehyde condensates, naphthalene formaldehyde condensates, gluconic acid, salts of low molecular weight, partially esterified styrene/maleic acid anhydride copolymers and copolymers of vinyl acetate and crotonic acid. The proportion of these in the pigment should preferably be from 2 to 6% by weight.
The above-mentioned dispersing auxiliaries act as liquefiers in concrete mixtures. They influence the water-cement ratio and have an effect on the consistency of the concrete.
In the inorganic pigment itself, the added binders act as foreign organic substances. According to DE-A 2 950 156, the inorganic starting pigment has a resin content of at least 20%. Distribution of the granulates in concrete is rendered very difficult by the resin contents of hydrophobic agglomerates.
Pigments which are free-flowing and produce little dust can be produced according to DE-C 3 918 694 but the free-flowing character and the amount of dust formation are not entirely satisfactory due to the high proportion of particles smaller than 100 .mu.m.
It is an object of the present invention to provide free-flowing, non-dust forming inorganic pigment granulates which are free from the above-described disadvantages of the state of the art for coloring building materials.